The objective of this research is to study the effects of environmental deprivation and malnutrition on child development and to establish to what extent it is possible to prevent retardation of physical and psychological growth by food supplementation and/or maternal tutoring. The relationship of malnutrition to impaired psychological function is confounded by health and social factors that covary with nutrition and may themselves affect psychological development. To investigate these complex relationships, a prospective multidisciplinary intervention study of children at risk of malnutrition was undertaken starting at 6 months of gestation. Families were assigned at random to 6 groups: A) No treatment controls; B) Supplementary feeding from 6 months to 3 years of age; C) Supplementary feeding from 6 months of gestation to 6 months of age; D) Supplementary feeding from 6 months of gestation to 3 years of age; A1) A home intervention program designed to increase maternal psychological stimulation of the child but no supplementary feeding; D1) Supplementary feeding from 6 months of gestation to 3 years of age plus psychological stimulation. All groups were given a uniform obstetrical and pediatric health care program. Subjects were observed longitudinally for the duration of intervention and for 3 years thereafter, through repeated measurement of nutritional status, intellectual functioning and a number of concomitant social and health variables. The field study composed the intervention and follow-up phases, was carried out in poor neighborhoods of Bogota, Colombia from 1973 to early 1981. Results to date show significant effects of supplementation on birth weight, physical growth, maturation and locomotor development while early stimulation affected cognitive performance and enhanced growth. The proposed analyses pertain to: a) intervention effects on cognitive, social and behavioral development at 3 and 6 years of age; b) intervention effects on diarrheal disease and the utilization of weaning foods during the first year of life; c) identification of sample subsets particularly responsive to the interventions; and d) group variations in developmental antecedent-consequence relationships.